Cabin pressure regulator



5- E. DEL MAR CABIN PRESSURE REGULATOR 2 Sheets-Sheet l INVENTOR.584/6! 1. 05.4 MAZ Feb. 23, 1954 Filed Feb. 14, 1951 Patented Feb. 23,1954 UNITED STATES PATENT QFFICE to Douglas Aircraft Company, Inc.,

Monica, Calif.

Santa Application February 14, 1951, Serial No. 210,945

6 Claims.

This invention relates to pressure regulating instruments and moreparticularly to such instruments especially useful in systems forcontrolling pressure of the air of pressurizable aircraft cabins.

This application discloses instruments of the one type disclosed in mycopending application Serial No. 669,366, now U. S. Patent No.2,549,673. in the pressure regulating system therein shown, as in allsuch. systems, the absolute pressure of cabin air is varied bycont-reliably varying the rate of air discharge from cabin relative tothe rate of air delivery to the cabin. The air delivered to the cabin isfurnished by superchargers or like blowers which are capable ofdelivering air to the cabin at pressures greater than ambient or flightpressure. The rate of discharge is varied by valve means controlling adischarge opening formed in the cabin wall.

Considerable development has been undertaken in the past towardproviding means to control the pressure in aircraft cabins along certainpredetermined schedules. Initial efforts were directed towardmaintaining cabin absolute pressure constant at an intermediate altitudewhenever flight above that altitude was attempted. Control of cabinpressure at the constant value of an intermediate altitude has beenfound impractical since it is obvious that little had been achieved inisolating the passengers of the cabin from the rather rapid changes inpressure during the ascents and descents in a region where the air ismost dense and where the pressure thereof changes most rapidly withchanges in altitude.

Control means have also been previously proposed which controlled cabinpressure in some predetermined relation to the change in pressure of theiiight atmosphere so that cabin absolute pressure was varied inproportion to changes in flight pressure. These prior systems, althoughan improvement over the constant altitude pres e schedules, did notprovide the most comer-table pressure change for the passengers as cacinpressure during ascent and descent still changed more rapidly at thelower altitudes than at higher altitudes.

The control instrument of the present invention in all embodimentsillustrated obviates the difficulties had with previous proposed controlI instruments by providing means for controlling the absolute pressurewithin the cabin as a straight line function of the altitude of theaircraft, that is, altitude used in the standard aeronautical sense asmeaning altitude based on absolute pressure in the standardinternational atmosphere. Where the term altitude is used herein it isintended to means pressure altitude in the sense just described.

The cabin pressure control effected by the control instrument of thepresent invention produces the slowest and, therefore, the mostcomfortable pressure change rate for the cabin passengers du' g descentsand ascents generally encountered in normal commercial aircraftoperations. This is true because the factor in controlling the change ofcabin absolute pressure during either ascent or descent of the aircraftis change oi altitude of the aircraft.

Since commercial aircraft have so-called ard or limit speeds, descentscannot be made faster than the rate which will produce the limit speedand it is conventional airline practice to descend in accordance withequal increments oi altitude per unit of time, Similarly on the ascentthe relatively constant available power from modern superchargedaircraft engines within the normal flight range makes it reasonable touse the excess power over that needed in overcoming level flightgravitational lift and drag forces to increase the aircraft altitude inequal increments per unit of time.

Thus the typical scheduled commercial aircraft climb or descent is oneof constant flight,

speed and constant rate of altitude change. Since passenger comfort inthe cabin may be measured in terms of pressure change rates, it isclearly most desirable to control the absolute pressure within the cabinas a straight line function of the altitude change of the aircraft.

In all embodiments of the instrument of the present invention a pair ofpressure change responsive means, one subject to cabin absolute.pressure and the other subject to changes in' cabin differentialpressure, coact together by so varying the rate of air discharge fromthe cabin relative to the rate of air delivery to the cabin as to causecabin absolute pressure to change as a straight line function of thechange of altitude of the aircraft. The cabin differential pressuremeans acts through a mechanism which opposes the action of the cabinabsolute pressure sensitive means on the means varying the rate of airdischarge from the cabin. This mechanism is so arranged that theinclemental effect of such opposition progressively increases thepressure altitude increases to so actuate the means controllably varyingthe rate of air discharge as to decrease the cabin absolute pressure ininverse straight line proportions to increase in pressure altitude ofthe aircraft.

Other features and advantages of the present invention will behereinafter apparent from the following description, particularly whentaken in connection with the accompanying drawing, in which:

Figure 1 is a perspective view of one form of the instrument with thecase thereof removed to more clearly illustrate the mechanism thereofand showing one form of a control circuit with which it can be used.

Figure 2 is an elevational view of one form of a dial face to be usedwith the instrument of the present invention;

Figure 3 is a schematic showing embodiment of the present invention andshowing the electrical circuits controlled thereby;

and v Figure 4 is a graphic plot of the pertinent pressure controlrelations between cabin pressure and flight altitude to more fullyexplain thepresent invention.

The embodiment of the" instrument of the present invention illustratedin Figure 1 comprises a housing or case, which for illustrativepurposes, has not been shown to more fully illustrate the mechanismforming the operating parts of the instrument.

The instrument includes a frame II'I formed at'one'end' thereof with anintegral wall element I I8 which closes the open end of the case whenthe frame is mounted thereinto. Fixed to the inner'surface of the wallelement II is a bracket member H9 for mounting one end of an aneroidcapsule assembly I2'I. The opposite end of the capsule assembly carriesa lug 22 for pivotally m mounting one end of a link I23. The oppositeend of the link I23 is pivotally connected to the free end of an arm I24of a bell crank lever pivotally mounted to arms I25 carried at oppositesides of the frame member II! and suitably insulated therefrom.

The arm I24 of the bell. crank lever is formed as a triangular platehaving a portion of the base thereof cut away to lighten the same. Theother arm of the bell crank lever actually comprises two arms I26angularly extending from the opposite portions of the base of thetriangular shaped arm I24. The outer or free ends of the arms I26 areinterconnected and held in spaced relationship by a cylindrical rod I21carrying at its opposite ends pivot pins I28 mounted in alignedapertures formed in the free ends of the arms I25. The cylindrical rod521 fixedly carries a'control arm I29, the one end of which is movablebetween and into engagement with a pair of'space'd contacts I31 and I32.

7 The contacts are insulatedly carried by lead screws I33 and I34threadedly mounted in a bifurcated element I35 carried at the one end ofan" elongate rod I36 the opposite end of which is pivotally mounted to'a bracket I 31 depending from the upper portion of the frame I I1. Theend of the arm I 35 pivotally mounted to the bracket I3! carries a,sector gear 538 meshing with the worm gear I39 c'oaxially mounted to arotatably mounted rod I4I. The opposite end of the rod I4I pierces thewall element H8 and carries at its free end an actuating knob, notshown, but used to rotatably drive the rod I4-I. It should be seen nowthat rotation of the rod [GI through the worm gear I39 and sector gearI38 will pivotally move the rod 36 about the axis established by itspivotal connection to the bracket I31. Pivotal movement of the rod I36;

results. in vertical movement of -the --bifur, cated of another element4 element I to conjointly adjust the position of the contacts I3I andI32 relative to the control arm I29. The control arm I29 is pivotallyconnected at the end opposite to the end portion engageable with thecontacts to a U-shaped link I42 by a pivot pin I43. The opposite end ofthe U-shaped link. I42 is fixed. to an. elongate pivot pin I44, theopposite ends or which are pivotally mounted in aligned apertures in ayoke I45 adjacent the bow or transverse element of the yoke. The freeends of the arms of the yoke M5 are pivotally connected by pins I46 to asupport element I41. The support element I4! comprises two t''riarigularshaped rigid frame members I48 fixedly inter-connected inparallelism by a web I49. The support element formed by the'fraine'membe'rs- I48 is pivotally mounted by pivot pins I 5| to fingersI52 upstanding from oppositely extending lateral arms I53 of the framemember II'I.

Rigidly carried by the one frame element I 48 is a sector gear I54meshing with a worm gear 255 coaxially carried by a rod I55 rotatablysupported in the wall element I I8 and projecting beyond the latter toterminate on the exterior of the instrument case. This end of the rodI55 carries an actuating knob I 5'1 for 'rotatably driving the rod I55which in turn, through the gears I55 and I54, 'ang'ularly adjust theposition of the support Isl from the solid line position shown inFigurel to the dotted line position of that figure. The purpose of thisadjustment will be hereinafter more fully explained. A capsule assemblyI58, similar to capsule assembly I3, has one end thereof rigidly fixedto the web element I49 of the support t ll while the opposite end ispivotally interconnected by a link I59 with the elongate pivot pin I44carried by the yoke I45. The interior of the case of the instrument isintended to be subject to cabin absolute pressure so that the exteriorof the capsule assembly I58 is exposed. to that pressure. The interiorof the capsule assembly I58 is to be connected to flight absolutepressurethrough a flexible conduit IBI leading to a hollowfitting I52carried by the frame member I I1 and presenting an opening I63 forreceiving an end of a tube or conduit, not shown, but leading to fiightabsolute pressure. The capsule assembly I58 is subjected to cabinabsolute pressure and flight absolute pressure and Williespond to thedifference between these pressures. The capsule assembly I58 is,therefore, a cabin differential pressure sensitive means.

The embodiment of the instrument now being described is intended to beused in a control circuit such as diagrammatically shown in Figure 1.Contact 3| is connected through a conductor I64 to a contact element I65forming a part of a receptacle member carried by the frame:

II! and adapted to receive an attachment cap to which lead 54 of thecontrol circuit, diagrammatically shown, forms a part. Contact I32 isconnected by a conductor I65 to contact member I6'Iadapted to-beelectrically connected to conductor 55 Ofth'e control circuit. A conducgear train, not shown, operates a valve 51 used.

to control the rate of air discharge from the cabin in=which theinstrument is'mounted. The mo:- tor 56 is reversible and may beenergized either through'the field coil 58 and 59 by-power from 5. somesuitable source such as a battery 6I to move the valve in alternatedirections depending upon the direction of rotation of the motor 56.

Automatic control of the valve 51 is effected through a control relay 62which, as shown for illustrative purposes, is essentially a poweramplifier in which very small currents from a battery 63 can be used toselectively energize the coils 64 and 65 of the relay 62 to control aflow of relatively large current in the circuits of the motor fieldcoils 58 and 59. Energization of relay coil 65 causes the armature 66 ofthe relay 62 to move to the left, as viewed in Figure 1, and intoengagement with a contact 61 against the action of one of a pair ofcentering springs 68 to complete a circuit from the battery 6| throughthe circuit of the field coil 58.

Energization of this field coil produces such rotation of the motor 55to drive the valve 51 toward closing position to decrease the rate ofair discharge from the cabin. Energization of relay coil 64 causes thearmature 66 of the relay to move to the right, as viewed in Figure 1, toengage with contact 69 against the action of the other of the pair ofcentering springs 69 to complete a circuit from the battery 6| throughthe field coil 59. The completion of this circuit, as should now beunderstood, causes the motor 55 to drive the valve 51 in the oppositedirection,

that is, towards open position to increase the rate of air dischargefrom the cabin.

As the conductor 55 interconnects through conductor I66, contact I3I andthe relay coil 64,

movement of the control arm I29 into engagement with the contact I3Iwill result in closing movement of the valve 51. On the other handmovement of the control arm I29 into engagement with the contact I32will result in energization of the circuit of the relay coil 64 whichincludes conductors I64 and 54 to produce opening movement of the valve51.

To explain the operation of the embodiment of the instrument now beingdescribed, it will be seen that as the aneroid capsule assembly I2Iexpands as the aircraft ascends, because of lessening cabin absolutepressure, the bell crank lever will be moved in a clockwise direction tomove the control arm I29 in a counterclockwise direction and intoengagement with contact I3I to energize relay coil 65 which, aspreviously explained, will result in closing movement of the valve 51.It will thus be seen that the aneroid capsule assembly I2I at somealtitude will tend to close the valve 5'! and attempt to maintain cabinabsolute pressure at a constant value as the aircraft ascends beyondthat altitude. If the aneroid capsule assembly I2I was the onlymotivating element operatively connected to the control arm I29, theinstrument now being described would merely maintain cabin absolutepressure at some constant value as the aircraft was flown at altitudesin excess of that altitude.

This is so, for it will be seen that as the valve 5'! moved towardclosing position, cabin absolute pressure would increase resulting incontraction of the aneroid capsule assembly I2I. Contraction of theaneroid capsule assembly l2l will result, as should now be understood,in counter-clockwise movement of the bell crank lever and consequentlyclockwise movement of the control arm I29 to move the latter intoengagement with the contact I32. Engagement between the control arm I 29and contact I32 would. as should now be understood, result inenergization of the relay coil 64 to produce opening movement of thevalve to lessen cabin absolute pressure. It will be seen that theaneroid capsule assembly will, therefore, tend to hold cabin. absolutepressure substantially constant at some" pressure value dependent, inpart, on the posl-- tion of the capsule assembly on the mounting bracketII9.

The differential pressure capsule assembly I56 also efiects the positionof the control arm I29 and in the embodiment of the invention now beingdescribed, as in the form of the instrument- 56 of my patent aboveidentified, mechanism is" provided for not only controllably varying thecontrol action of the differential pressure cap-'- sule assembly I58 onthe control arm I29, but"- to also obviate any control action by thedifferential pressure capsule assembly as the same ex-' pands orcontracts.

It will be seen that so long as the support I41 is in the positionillustrated in solid lines in Figure 1, the axes of the pins I 43 andI46 are coincident as are also the axes of the pine I 5I' and I44. TheU-shaped link I42 is of such a length relative to the length of the yokeI45 that with the pins aligned, as above described, expansion andcontraction of the difierential pressurecapsule I58, although resultingin pivotal movement of the yoke 15 and U-shaped link I42, will nottransmit movement to the control arm I29; This is so for both the yokeand the U-shaped" link I42 will pivot about a common axis established bythe axes of the pins I46 and I43. With, the support I4? in the positionshown in solid lines in Figure l, the control arm I29 is substantiallylocked against movement regardless of changing cabin differentialpressure and is subject only to the control action of the aneroidcapsule assembly I2I. y

If the support I4! is moved to the dctted'line position shown in Figure-1, the lower end of: the yoke I45 remains in substantially the positionshown in solid lines, while the free ends of the arms thereof pivotallymove into the position shown in broken lines. This movement of thesupport I41 does not in any way eifect the posi'- tion of the U-shapedline I42, which in all positions of adjustment or" the support I41remains" in the position shown'in Figure-l.

With the support :41 and the yoke I45 new;

moved to the position shown in broken linesin Figure 1, it will be seenthat expansion and con-J traction of the diiferential pressure capsuleassembly I58 will, through the link I59, arcuately move the yoke I45about the axis established by the pins I46 which are now no longeraligned or coincident with the axis of the pin I43. The capsule assemblyI2I, in expanding as the air-.' craft ascended, would result in anelevation of cabin absolute pressure over flight ambient pressure toproduce an increasing cabin (inferential. pressure. This brings aboutcontraction of the capsule assembly I58 and the link I59 applies athrust to the left against the yoke I45'to:

arcuately move the yoke in a clockwise direc-.. tion about the axes ofthe pins I46, resulting in clockwise movement of the U-shaped link 142about the axis of the pin I43. of the link I42 applies an upward thrustto theleftward end of the control arm I29 to move the control arm in aclockwise direction about the axes of the pins I28 to move the control,

arm into engagement with the contact I32 which it will be remembered,results in opening move This movement olookwise direction about thexesof the ,pins

1.2-8- to;move the control arm I29 into engagemcl l; With'the contact13! which, it. will berememberedbrinssabout. closin movement of the vale andr onseuuentlyra in rease in cabin absolute pressure.

' It will thus be seen that thedifierential pressure capsule assemblyI58 opposes theaction of the aneroid capsule-assembly on the control arm123. The ratio mechanism formed by the Uz -shaped link M2 yoke 145,support element M1randassociatedconnector elements is so arranged thatthe incremental affect of the-opposition of the differentialpressurecapsule 158 progressively increases "as the pressure altitudeclothe aircraft increases.

v They-resultant control action on the control arm I29;heQauSe-Qfthe-ccaction between the interconnected capsule-assemblies I58and m, brings about/such movement of -the control arm into andloutofengagement-withthe contacts l3| and 32 thatcabin absolut pressure iscontrolled as;.a. straight line functionof thepressure altitude ofthe-aircraft. Cabinabsolute pressure is, therefore, actuallycontrolledto decrease in inverse Qstraight line proportions to increase inpressure altitude of the aircraft.

- .Theinstrument a sh wn F gure may b urovidedwith-adial and handarrangement such asshbwnin Figure 5 of my Patent No. 2,548,673 which fiure has been reproduced here as Fig- 111.112! ,Tdsimp ify th illustratiof this mbod rderitof-th invention thegea-r trains interconnectingthered I 56 and! have not been shown. The instrument of. Figure l differsfrom the instrument .56 of .mypatent ,above identified in that noadjustment is provided for moving theaneroid capsule assembly -l nceithas be n m unt d tothebracket member. The equalizin altitude settingwith the instrument shown in Figure l ishccomplished through movement ofthe contactsliil and 132 throughrotation of the rod liiiandthe ar trainvfonn dln t e Worm gear resend the sector-sea m shin th rewith.

. ,To more v.fully. describe the control action of theinstrument of thepresent invention, there isshown in Figure 4 graphic illustrations ofpressure vschedules controlled by the instrument ofjthe presentinvention. The pressure of the standard atmosphere as a function offlight altitudeisindicated' by the curve I06 and so labeled. Flightaltitude is sealed in thousands of feet abscissa and pressure is scaledin inches of mercury' absolutealong the ordinate of the graph. Thecontrol instrument of the present invention wouldibc usedwith anotherinstrument also operatively connected into thecontrol systemdiagrammatically shown in ..F.igure l, to control opera n of the motornd consequently the valveto prevent cabin differential pressure fromeaceedine some pr de ermine max u differential determined .by thestructural strength of the cabin. For illustrative purposes there shownin- Figur a-curv 4:01 nd catinethe limit, cabin difierential pressure.of-8.5 gin. w h r spe to he t o pheric-P essure. ,This limitdifferential pressure is constant so that the vertical o r in distancebetwe n this-rem and the a mosph ic p e su e urve is. a-constant fixedquantity r all .fiieht alt tu e The curve Ill-8 of the graph of Figure-erep.- resents one possible control schedule wit; -.the instrument f h prs n n enti n. time repr sent a he ul .o bin pre s re during, transitionof flight altitude from 200.0 wfeet; to. 1,1.600ieet and for thisschedule cabin -;pres,sure will remain constant at a'value (27.82 inchesof mercury absolute during flight between thesealtitudes.

To bring about a cabin pressure control; schedule such. as, representedby thecurve .108, the instrument would be adjusted throughirotation ofthe rod to provide an equalizing. altitude setting of 2000 feet. This,adjustment, as should now be clear, would conJ'Ointly.rnovzev contactsI31 and H2 upwardly, as viewed in Figure 1, to bring contact i312 intoengagement. with the control arm I29. As previously -ex-. plained,engagement of contact .132 with the controlarm I29 energizes the valveopeningfiii cuit of the motor 56. Under'this'cabin pressure controlschedule the support element 44-! would. occupy the position shown insolid lines ure 1 and would not be. operative t0. Q l2 :I Q- ment of thearm I29.

With the instrument setas above described-the aneroid capsule assemblyI21, so .long as :the aircraft did not-exceed an altitude of 20.00 feet,would remain sumciently collapsed'to hold .the control arm in engagementwith contact 132. The valve wouldconsequently-remain openand cabinpressure would follow atmospheric pre sure as the aircraft ascended.When the air? craft had ascended to an altitude of 2000 feet, theaneroid capsule assembly I62! woulcl inexpanding because of lesseningpressure, move. the control arm E29 out of engagement with the .60 tact132. As the aircraft continued .to ascend, the aneroid capsule assemblyingfurther expand. ing would move control arm in into engagement withthe contact I35 which, it will be .remembered, completes thevalveclosing ciliguitof the motor.

As soon as the ,valve commenced its-closing; movement, cabin absolutepressure would increase which would bring about acollapsing ac.- tion of:the aneroid assembly to move the-control arm out of engagement withcontact 132.. If abin absolutep sure cont nued to in rease. the controlarm would be moved into engage ment with contact E32 to energizethevalve Q1381}:- ing circuit of the motor 56. The control arm 2'29 would,therefore, under the control action of the aneroid assembly l-2l act toeflect op-1 eration of the valve such that cabin absolute.-pressurezwould be maintained at a simulatedi20fl0 feet altitude as theaircraft continued to ascend.

It should -.now ice-obvious that if an apparent cabin .altitude of say6000 feet'was desired to be maintained in the-cabin, such-asrepresentedby the curve 1 ii] in Figure 4, "the instrument would be adjusted bymanipulation of the rod its to set the contacts 13'! and 132 in the'position to bringabout an equalizi g altitude set-- ting of 6000 feet.Here again the support ele.-

ment 'l'd'l would be maintained .in the position shown in solid. linesinEigure. .1 to obviate-any control would be clearly applicable.

control action by the differential pressure capsule assembly I58 on thecontrol arm I29.

Control of cabin pressure in accordance with a schedule along any one ofa plurality of sloping curves such as control curves III and H2 can bepresented by a fractional ratio. An ordinary ratio control would berepresented by the following (P) (cabin absolute pressure) (P) (flightabsolute pressure) l where P is the flight absolute pressure at thepressure altitude at which pressurization of the cabin is to begin, andk1 is a predetermined 'to consist of two coacting aneroid units, onesensitive to cabin pressure and one sensitive to flight pressure, thenthe above expression for the ratio However, since the instrumentcomprises an aneroid sensitive to cabin pressure and a differentialpressure capsule exposed to the difference between cabin pressure andflight pressure, the above expression may be more clearly applied in theform:

(P) (ca in absolute pressure) k (Cabin absolute pressure) (flightabsolute pressure) 2 where P is the flight absolute pressure at thepressure altitude at which pressurization of the cabin is to begin, andk2 is a predetermined constant which for example may have a useful rangefrom to 1.5. The expression for k1 and k2 define identical schedules ofcabin pressure in that they each represent a straight line when plottedon a graph of cabin pressure as one ordinate and flight pressure as theother ordinate.

In Figure 4, the form of cabin pressure control in which the change ofcabin pressure is a direct ratio to the change of flight pressure isrepresented by the sloping curve II! and H2. The sloping curves,although straight when plotted on a graph of cabin pressure as oneordinate and flight pressure as the other ordinate are not straight whenplotted as in Figure 4, V -but=are bent with a greater slope at loweraltiation of the aircraft, climbs and descents are normally gauged byinstruments which read in terms of altitude.

should be controlled at a minimum rate in relation to the pressurealtitude variation of the aircraft and not its flight pressurevariation. This type or" control can be best defined by its straightThus, for the greatest comfort to passengers, the change of cabinpressure line relationship in Figure v4 but can also beexpressed:

(P) (cabin absolute pressure) where P is the flight absolute pressure atthe pressure altitude at which pressurization of the cabin is to begin,and k3 is a predetermined constant. If pressures are expressed in inchesof mercury and altitudes are expressed in thousands of feet, the usefulrange of this ratio It: is from 0 to about .00007.

The equations for k1 and k2 represent a ratio to flight pressure controlwhich can be defined as a straight line on a graphic plot of cabinpressure as a function of flight pressure. The equation for R3represents a ratio to flight pressure control which can be defined as astraight line on a graphic plot of cabin pressure as a function offlight altitudes. Two other forms of ratio control are similar to thetwo previously mentioned but as should now be understood are far lessdesirable. These are, first, one which plots a straight line for cabinaltitude varying as a function of flight altitude, and secondly, onewhich plots a straight line for cabin altitude varying as a function offlight pressure.

The straight curves H3 and H4 are then preferred control schedules tothat shown by the sloping curves III and I I2. However, since thefractional expression for the ratio 761 in the sloping curves is simpleto express, this general ratio notation will be used for the ratio toaltitude curves. For example, as shown by the table in Figure 4, thesimplified approximate value of the ratio for curve H3 is A; or .25. Itsexact value would have to be expressed by k3.

Control curve II 3 represents a schedule of cabin pressure duringtransition of flight altitude from 2,000 feet to 15,500 feet and forthis I schedule, cabin pressure is seen to vary from a value of 27.82inches of mercury absolute (2, 0

feet altitude) to a value of 24.98 inches of mercury absolute (4,900feet altitude) during flight from 2.000 feet to 15,500 feet.

To bring about a cabin pressure control schedule such as represented bythe curve H3 in the graph of Figure l, the knob carried by the rod I36would be adjusted until the dial of the instrument read a pressurizingaltitude of 2000 feet. This adjustment, as should now be clear, wouldconjointly move contacts I3I and I32 upwardly, as viewed in Figure 1, tobring contact I32 into engagement with the control arm I29. Aspreviously explained, engagement of contact I32 with the control armI29v energizes the valve opening circuit of the the motor 55. Throughmanipulation of the actuating knob I51 the support element I 5? carryingthe capsule assembly I58 would be moved to a position in which thedifferential pressure capsule assembly would be operative to oppose theaction of the aneroid capsule assembly HI and conjointly act therewiththrough the ratio mechanism tocontrol movement of the control arm i20.As in the operation of the embodiment of the instrument 56 of my patentabove identified, the hands of the instrument would be moved to indicatea limit flight altitude of 15,500 feet and a ratio limit cabin altitudeof 4,900 feet.

With the instrument set as above described, the aneroid pressure capsuleassembly I2 I, so long as the aircraft did not exceed an altitude of2000 feet, would remain sufliciently collapsed to hold the control armI29 in engagement with the conarrangement the ratio mechanism,

tact-132; As-the aircraft ascended to. analtitude of 2000 feet theaneroid capsule assembly: t2! would in expanding move the control armI26 out of engagement with the contact I32; the aircraftascended'beyondan altitude of 2000 feet, the aneroid capsule assembly infurther expanding :would move control arm- I29 into engagement with'thecontact I3 1- which; it willberemembered, completes the valve closingcircuit.

As soon as the valve 51 commences to incve toward closed position, cabinabsolute pressure will immediately tendto increase'over flight absolutepressure and cabin diiferential capsuleiassembly-I58 will contract andthus move theyoke I45 in aclockwise'directionabout the axesof the 5 pinsI46. This in turn produces'clockwisev move.- ment of the U-shapedlinkI42 about the; axis of the-pin I63,as previously explained; to apply anupward thrust to the leftward end of the. control arm I29 to move thecontrol arm into engage ment with the contact. I32 and thus open thevalve 51 to consequentlydecrease cabin absolute pressure.

Because of the geometrical and kinematical cabin absolute pressure willchange as a straight line function indicated by: the curve H3 as-thepressure-altitude of the aircraft. increases totthe altitude indicatedby the ratio limit flight altitude hand, that is: 15,500'feeti Controlof the valve, as the aircraft continues to ascend, would be underthe'controlof adifferential pressuremechanismforming. a part of thesystem, but not herein shown or described.

Again it is'not believednecessary to explain how the instrument isadjusted: to set the same to' bring about the pressure schedulerepresented by the curve I I4: Any number-of pressure schedules-can bebrought about merely by adjustment of: the knobs carried-'bythe-rodsIlia-and I56; It is'tobe remembered, however, that the schedulespossible-with the instrument of the present invention would be alwayssubject to the limiting action of the difierential pressure limitcontrol instrument which is at all times operative to limit cabindifferential pressure to some-selected value such as represented bycurve I01 and determined by the structural strength of the-cabin.

There'is shown in Figure 3 an instrument schematically indicated at HIwhich..-includesa control arm I12 pivotallymounted'as-indicatedat I13.The embodiment of the instrumentshown in Figure 3 includes an aneroidcapsule'assembly and differential pressure assembly, not shown, butwhich will-coact through a: ratio control mechanism of theformshown inFigure 1 to'move the; control arm: I12'in opposite directionsdepending'upon the relationship of cabin absolute pressure'to flightpressure altitude;

The control arm I12carries at its'outer or'free end a core elementIMarranged transversely of the arm I12; The: opposite end portions' of:the coreelement fi l are-'coaxially disposedwithin space coils I15 andI16 seriesconnected into'a circuit I 11 which includes a source ofalternating current I1 flan'd a manually operable switch" I19.Arrangedadjacent'the coi1sI15and I16 arecoils Hand I82 respectively, soformedthatone or the other of'theopposite end portions of the coreelement I14 will traverse the turnsof' one or the other of these coilsasthe arm I12ispivotally-moved in one direction or the other-under therurgings of the pressure change responsive capsule assembliesinterconnectedswithr the arm H2. The coil IBI -is series connectedfwith'a coil 1-12 I 33': while coil I82; isconnectedi with a similar-coilI84. The coils: I83 and. lt -lcircumscribe' the opposite ends of av coreelement I 85 mounted for longitudinalv movement but yieldably heldby-centering springs'lflfi; similar to springs 68 0f "the previouslydescribed-control circuit-in a 'center'or neutral position;

The-normal position of the core element-185 15 shown in Figure 3 and inthis position the opposite end faces thereof are spaced from. fixedcontacts I81 -and I88 connected respectively, by leads I89 and HI tofield coils I92 and I93 of a reversible motor I94 similar to the motor56 of the controlasystems of thezpreviously' described embodiments .of?Ithepresent invention: The circuit of themotor I94 includes arsource ofcurrent such as'the'battery I 95 groundedi'as indicatedzat l 96.

The motor" I slldrives, through a suitable-gear and; link m'echanism'indicated at I91; an airzexhaust. orr'discharge valve I98 regulating therate of airdischarge from the cabin; As the motor is reversible;depending: .up'on-fthe field coil enere gized, the motor will drivethevalvein opposite directionstofeithenincrease or decrease the rateofrair dischargefrom the cabin. Energizationpf themotor'field COiI'IIQZresults in such" rotational movement'of themotor' I94 asto movethe-valve I 08:: toward closed position. while energizati'on of thefield coil. I93 results. in opening: m'ovementzof theva'lve I'98."

In. the operation of? the instrument now being described, if 'the'arm' I12 is moved iniethe direction of. the arrow I 99; the :onerend. portion:.of the core element 114 progressively transverses the turns of the coil$81 to induce. inv that coil and consequently coil I33 anelectro-magnetic flux. suificient to draw or attract the coreIS5'upwardly and into engagement with the contact I81. As the core I85is grounded,. as. indicatedi at 20: 2, movement of thecoreev liifirinto:engagementi'with the contact' I81will complete a" circuit from .thebattery I 95 through the motorfield coil: H92 which, aspreviously-explained, results-ma closing movement. of the valve I98;

On the other'hand', if the arm I12 ismovediin the directionzof the arrow2 02.; the one end portion of i the; core element. I14 moves-between theturns of the: coil I82 and the current: induced inthat coil andconsequently thecoil; I84 will draw. the core: element I85:downwardly-'as viewed in Figure 3-and into engagement: with" thecontactxIBS; It should nowbe obvious: that-"engagementof. the coreelement:.l85 with the contact'ltil energizes the motor fieldrcoil I93itoproduce opening movementcof the valve: I198.-

It is: not believed necessary to explain how the instrument of Fig-ure3'can beused' to bring about the; pressure schedules indicated by' thecurves H3 and H 3 as actually'tl'isrinstrument will op erate inexactly-*the-same manneirasthe"embodiment of the; instrument: shown in'Iligure'l. As thecontrol action of that instrument has been explained indetaiLit.should be-clear nowhow the. instrument of Figures will bringabout the desired control of. cabin. absolute pressure.

Although all embodiments of the presentinvention have been herein shown.and described as instruments controlling electricalsystems, it should beobvious that by very slight modifica tion the instruments herein. showncould be used with other types of motivating systems; Hydraulic orpneumatic motivating systems could be'us'ed with the instruments of thepresent invention if such systems were preferred to the electrical .onesherein illustrated;

'13 7 Actually the particular type of system is not important to theinstruments of the present in- Vention and the electrical systemsillustrated have been selected merely to further explain the conthepresent invention have been illustrated and disclosed, herein, it is tobe understood that the invention is not to be limited thereto for it issusceptible to changes in form and detail within the scope of theappended claims.

I claim: 7 1. A pressure regulating device for use in a -'system forregulating'absolute pressure within an aircraft cabin whereinto air iscontinuously supplied by an air delivery means and from which vitiatedair is discharged through a controllable outlet valve, comprising:actuator means to be 'operatively connected to the control means forsaid valve; a first capsule responsive to changes in cabin absolutepressure; first link means, including a bell crank lever, operativelyintercomnecting said first capsule and said actuator means whereby saidactuator means is moved in response to changes in cabin absolutepressure to regulate the valve control means to maintain cabin absolutepressure substantially constant above a pre-l selected pressure altitudethereby to create a cabin differential pressure above said preselectedpressure altitude; a second capsule responsive to changes in thedifferential between cabin absolute pressure and flight absolutepressure; means for pivotally supporting said second capsule whereby thedirection of movement thereof as the same responds to changes in saiddifferential may be varied; second link means operativelyinterconnecting said second capsule and said actujat'or means, saidsupport means being movable to so position said secondca'psule that thelatter,

as cabin diiferential'pressure changes, so moves said second link meansas to oppose the action of said first capsule on said actuator means,said second link means being'so arranged that in the said one positionof said second capsule the incremental effect of such oppositionprogressively increases as the pressure altitude of the aircraftincreases to so actuate said actuator means as to regulate the valvecontrol means to decrease cabin absolute pressure in inversestraight-line proportion to increase in pressure altitude of theaircraft. 2. An instrument for use in a system for regu' lating pressurein an aircraft cabin, which system includes means to effect and controlair outflow from the cabin comprising; a housing to be mounted withinsaid cabin and including means for communicating the interior of saidhousing with the interior of said cabin; a rigid frame element removablymounted within said housing; an evacuated capsule mounted to said frameelement, said capsule exteriorly subject to cabin absolute pressure, andmovable in response to changes in cabin absolute pressure; a

support element pivotally mounted to said frame element; a secondcapsule carried by said sup-- port element and movable therewith;meanscarried by said housing adapted to-be connected t'd-flight absolutepressure and communicating 14 with the interior of said second capsulewhereby the latter is to be subject to, and movable in response tochanges in, the difierence between cabin absolute pressure and flightabsolute pressure; control effecting means, including means adapted tobe operatively connected to the means of said system for effecting andcontrolling outflow of air from the cabin; means operatively connectingsaid first capsule to said control eifecting means whereby the latter ismotivated by pressure change responsive movements of said first capsule;a linkage mechanism interconnecting said second capsule and said controleffecting means; means for pivotally moving said support element to varythe position of said second capsule relative to said linkage mechanismto thereby vary the operative connection between the said second capsuleand said control efiecting means, said linkage mechanism in one positionof said second capsule opposing the action of said first capsule on saidcontrol efiecting means and being so arranged that the incrementaleffect of said opposition progressively increases as the pressurealtitude of the aircraft increases to produce such motivation of saidcontrol eifecting means that the latter is adapted to control operationof said outflow effecting and controlling means of said system to varycabin absolute pressure in inverse straight-line proportion to decreasein pressure altitude of theaircraft.

3. An instrument for use in a system for regulating pressure in anaircraft cabin, which system includes means to effect and control airoutflow from the cabin comprising: a housing to be mounted within saidcabin and including -means for communicating the interior of saidhousing with the interior of said cabin; a rigid frame element removablymounted within said housing; an evacuated capsule mounted to said frameelement, said capsule exteriorly subject to cabin absolute pressure, andmovable in response to changes in cabin absolute pressure; a supportelement pivotally mounted to said frame element; a second capsulecarried by said support element and movable therewith; means carried bysaid housing adapted to be connected to flight absolute pressure andcommunicating with the interior of said second capsule whereby thelatter is to be subject to, and movable in-response to changes in, thedifference between cabinabsolute pressure and flight absolute pressure;control effecting means, including means adapted to be operativelyconnected to the means of said system for effecting and controllingoutflow of air from the cabin; means operatively connecting said firstcapsule to said control effecting means whereby the latter is motivatedby; pressure change responsive movements of said first capsule;andlinkage mechanism, including link means pivotally mounted to saidsupport element, operatively interposed between said second capsule andsaid control effecting means and 'operatively connected at the one endto said second capsule and so organized geometrically and kinematicallywithin itself as to respond linearly and integratingly to the motions"of bothsaid capsules to progressively and decreinentally modulate theresponse of said first cap mile to changes in cabin absolute pressure ascabin differential pressure increases therebyto so motivate said controleffecting means that the latter is adapted to control operation of {said"outflow effecting and controlling means ofsaid system to constraincabin absolute pressure to amen-cal *ifoi'IoW- a straight: linefunction--v of:- the 2 pressure altitudes! tlie1 aircraft:

An in'strumentifor use Lima-system :for: regulating :pressure inandaircraft cabin,- which systemzincludes means to efiecttand-controlair.out-- new from the cabin comprising: a-l'iousing to be mountedwithin zsaidricabin andiincluding means Ion communicating the interiorof said housing withithe interior OfESaid cabin; a rigid frame-ele-.mentt removably mounted: within said 1 housing; an': evacuatedcapsulesfixedly mounted. to said 'frame element; exteriorly subjecttocabin absointer-pressure; andimovabiei in response-to changes cabin.absolute" pressure; a support element pivota-lly mountedi to said iframe element; 1 a secondticapsule carried :by' said "support element'an'd .1 movable therewith; means: carriedtby saidzhousing:adapteditobecomiected to-fiight absolute pressure? andcommunicating:with the: interiorof said; second capsule whereby thelatter: is to be subject to andmovablein response'to changes "in the:diiierence between cabin absolute pressure and flightabsolute (pressure;a control arm; control means, including means adapted totbetoperativelyconnected'ito the means of' said system'for- 'effecting 'and controllingoutflow of air from the cabin,"- and opera-tively coacting' with saidarm to control operation: of said outflow means: means: operativelyconnecting said r first capsule to said" control'arm'vwhereby the latteris motivated by pressure change responsive movements ofisaidfii'stcapsule; means for variably positioning-said oontrol means+to varythe motivaam of the same as said' first capsuleimoves in response-150changes-in cabin absolute pressure; a linkagemechanisminterconnecting said second capsule an'd said controlefiecting' means; and means ior*'pivotally moving" said support elementtovvary the position i of 'said' second capsule relative to said'linkagemechanism to thereby-vary theoperative connection by the saidsecond capsule and said control effecting" means, said linkage mechanismin one-position of said second eapsule opposing' the action ofsaidflrst' capsule on: said control" efiecting means d being 80 arrangedthat the incremental effect of said opposition progressivelyincreases;as the'pressure altitude ofthe aircraft increasestoproduce'such motivation of said control effecting means that thelatter is adapted to control operation of" said outflbw effe'ctingandcontrolling means of said system tb vary cabin absolute pressure ininverse 'sti'aiglit line' proportion to decrease inpressure altitude ofthe" aircraft.

1' 5.- An' instrumentfor use ln a system fol-regulatiiig'pressure inanaireraft cabin; systeminclud'es means to effect and controlair-outnew: from the oabincomprising: a; housingto' be mounted within:said: cabin andxincluding means vfor; communicating the interior: ofsaid housing with;theinterior ofsaid cabin; a rigid frameelementzremovably mountedivithinisaid housing; an

' t6 luteapressure; icontrol eiiectingiimeans; includin n'ieansr--adapted" bea operatively connected to the means" of: saidsystem afor:efiecting and con.- trolling outflow oiz'airz fromlthe cabin; meansoperatively connecting said first capsulesto said control; enactingmeansawhereby thelatter is motivated by pressure changeresponsivamoverments of saidsfirsticapsulegg a yoke; means-pivotally:connecting .the-freaends of said:yolre,v to said. support: element"; a.-pin carried; between; thewlegs of said yoke: adjacent the 1transverse.-. member thereof; a link pivotaJlyvintercon-nectingsaidseoeond' capsule? andsaid'pm; and a-U-shapedlink pivotal'ly; connectingthe-:onesend to said pin and at the: opposite; end to"; said controlreflecting means; said yoke and link forming at linkage mechanism soqorganizedrgeometrically and .lcinematically within itself @as: torespond linearly and integratingly to the motions of both saidscapsulesto progressively-and decrementally: modulate :the

responsesof said .firs-ticapsule-to; changes inscabin absolute.-pressureas cabi-mdifierential pressure increases-:- thereby? to so,motivate. said, control efiecting .means-thatzthe latter. is adapted to7 control operation. of.) said outflow effecting and con,-trollinglmeansr of. said system 7 to constrainzcabin absolute; pressurev:tmfollow a straight .line. function oi. the pressure altitude-oi theaircraft.

6; An' instrument for. use in a system-ion regulating pressure in. anaircraitcabim. Which-1, system includes means :to .efiect. and-controlair-outflow from the cabincomprising ahouslng to be mounted within saidcabinsand including means for communicating. the interior of l.saidhousing with the interior ofssaid-cabin; a rigid lframeselementremovably mounted. within said: housing; an evacuated capsulefixedlymounted. to, said frame element, exterior-1y subjectetocabinlabsolute-pressure and movable :iIlzI'BSDGIlSB to changes in cabinabscluteupressure; a support. element pivo-tally -mounted to said frame;:elementi. a secand capsule carried .by; said supportelement ,andmovable therewith; l means carried by saidihousing adapted to beconnected: to flight absolute pressure anclcommunicatingw-ith the.interiorrof said second.capsulel whereby the latter, is to besubjectzto and movable; inresponseeto; changes. in the differencebetween cabins absolute; pressure and flight absolute pressure;control,v effecting means, including means adapted tobeoperativelyconnectedtotthe means .of. .said system;.for,- effect- 111g;andlcontrolling outflow l of l air .irom the cabin; means operatively,connectingflsaid first capsulelto said control;- effecting meanswhereby; the; latter is motivatedmypressure change responsivemovetion ofthe same as said first capsule movesin response tochanges incabimabsolutepressur; alinkagemechanism.interconnecting.said secondcapsule: and? said: control effecting means; and means; for pivota1ly,-moving said. support element to: vary the :positionofsaid second capsulerelative to said linkage mechanism to -thereby,- vary the operativeconnection. between said; econd capsule; and said;- control efiectingi.means,- v said linkage mechanism in; one. position of said: sec ond:capsule opposing the, action of said: first capsule onsaidcontrolvefiectingameans and,being so arranged. that the incrementaleffect of; said opposition progressively; increasesas-the pressurealtitude of; thevaircraftvincreasessto, produce; such motivationof:saidscontroleefiecting means that thealatter iss-adapted-to;controloperation' of :said outflow efiecting. and controlling: means of;said system to vary cabin absolute pressure in inverse BRUCE E. DEL MAR.

References Cited in the file of this patent Number Re. 23,536

UNITED STATES PATENTS Name I Date Del Mar Aug. 26, 1952 10 Number 18Name Date Noxon Mar. 5, 1946 Bechberger Sept. 28, 1948 Widgery et a1.Mar. 1, 1949 Del Mar Apr. 17, 1951 Klemperer Apr. 17, 1951

